Gemstone Lapidary
The steps taken to produce faceted gemstones are: - Sawing, Grinding, Sanding, Lapping, Polishing, Tumbling
Sawing - A thin circular blade, rotates at several thousand surface feet per minute literally scratches its way through a gemstone. A liquid such as oil or water is used to wash away cutting debris and keep the stone and the saw blade from overheating. Several sizes of circular rock saws are frequently used by most gemcutters:
- A slab saw, typically 16 to 24 inches in diameter
- A trim saw, typically 6 to 10 inches in diameter
- A faceter's trim saw, typically 4 inches in diameter
Grinding - Usually with silicon carbide wheels or diamond-impregnated wheels, grinding is used to shape gemstones to a desired rough form, called a preform. As with sawing, water or oil is used to remove debris and prevent overheating.
Sanding - The purpose of sanding is to remove deep scratches left by coarser abrasives during grinding. Since it removes material less rapidly, it also allows more delicate control over final shaping of the stone prior to polishing.
Lapping - Lapping is performed on one side of a rotating or vibrating flat disc known as a lap, and it is used especially to create flat surfaces on a stone (as in faceting). Laps are often made of cast iron, steel, or a copper-bronze alloy, but other materials can also be used.
Polishing - Gemstones are usually polished to a mirror-like finish to aid light reflection from the surface of the stone (or refraction through the stone, in the case of transparent materials). Polishing agents are metal oxides. Rounded surfaces, such as on cabochons, are often polished on felt, leather, cloth, wood or cork.
Drilling - A small rotating tube or rod with a diamond tip is used to drill through a stone. Ultrasonic, or vibrating, drills are also very effective, but are costly and thus reserved for high-volume commercial drilling.
Tumbling Tumbling is the rotating of a barrel, often hexagonal in shape, with abrasives and water and roughly shaped stones. Large quantities are tumbled for long extended periods of days or weeks. The stones are gradually smoothed and polished to serendipitous but often very attractive shapes. A vibratory tumbler is often used as an alternative, where the containing barrel vibrates rather than rotates. Where standard tumblers must be halted in order to check progress, the stationary arrangement of vibratory machines makes it easier to examine the progress of the stones inside.
Intrasias and Mosaics - Small bits of different colored stones are fit together and the top cut and polished to present a picture or other interesting pattern. A mosaic is constructed on top of a flat base of another material and intarsia is set flush into the surface of the base material.
Cameos and Intaglios - Cameos are raised portraits and Intaglios are carved down into the surface of the material. Both typically take advantage of different colored layers of material.
Sculpture - Gemstones can be carved into almost any form. Carving is accomplished with a variety of diamond-impregnated steel bits, saws, and grindstones.
Faceting is most often done on transparent stones. Flat facets are cut and polished over the entire surface of the stone, usually in a highly symmetrical pattern. The cutting angle is adjusted vertically via a protractor and rotationally via an index gear. The facets are then ground, sanded, and polished on a rotating lap, while water or another liquid acts as a coolant and lubricant.
Cabochon - Cabochon is one of the simplest of lapidary forms. The stone is smoothly rounded and polished on top, relatively flattish, and either flat or slightly rounded on the bottom. This form of cutting is often used for opaque or translucent stones. Coloration and patterning provide the major interest in such stones. Cabochon cutting or cabbing; is often performed by holding the stone in the fingers, but it is more commonly done by dopping. This facilitates twirling the stone to form smooth curves and avoid flat areas during grinding, sanding, and polishing.